1. Field of the Invention
The invention relates generally to hairdrying appliances. More particularly, the invention relates to heater sections used in hair dryers for generating heat.
2. Description of the Prior Art
Hair dryers for drying hair generally comprise a motor for driving a fan to blow air past heated coils of resistance wire. The motor, fan and resistance wire are included in a dryer housing which may be attached to a handle and the hot air is blown out of a nozzle in one end of the housing.
The heater sections of prior art dryers generally comprise resistance wire spirally wrapped about an electrically insulated support frame made of, for example, mica boards and axially interposed in the air stream generated by the fan. One such heater section using coils of wire wrapped around a support board is shown in U.S. Pat. No. 4,260,875 assigned to the assignee hereof. In this type of construction the motor is mounted upstream from the support frame. Another type of heater section comprises a single continuous length of sinusoidally shaped resistance wire (as opposed to a coil) spirally wrapped around a similar frame. In these embodiments the frame consists of a conventional crossed pair of mica boards. The radially distal edges of the mica boards are notched in a saw-tooth pattern to receive the wire which is then connected at predetermined points along its length to a current source. The wire may obviously be connected to the current source at each end to generate the maximum heating ability and various portions of the wire may be connected to a current source by means of taps interposed along the length of the wire.
Another type of known heater section utilizing spirally wound, sinusoidally shaped wire includes a hollow cylinder axially aligned with the air flow and having a plurality of insulating boards radially extending from the external surface of the cylinder with the wire wound around the exposed edges of the insulating boards. In this embodiment the motor is situated within the cylinder with the motor output shaft and attached fan extending from one end of the cylinder.
Both of the aforementioned types of heater sections are inefficient in the distribution of heat at the nozzle output of the hair dryer. Because the resistance wire is essentially concentrically wound about the axis of the hair dryer near the interior of the housing, the air coming out of the nozzle is relatively cool along the axis and extremely hot near the edge of the nozzle. This type of unbalanced temperature distribution occurs in conventional coiled resistance wire heaters as well as those utilizing sinusoidally shaped wire wound about a cylindrical core.
The extremely high tenperatures near the edges of the nozzle create an obvious safety hazard. Such an uneven temperature distribution also necessitates careful selection of the material of the nozzle to enable it to sufficiently withstand such extreme temperatures (on the order of 250.degree. C.). Moreover, such an inefficient temperature distribution necessitiates operating the resistance wire at an unacceptably high level of current in order to produce an acceptable overall temperature output from the hair dryer. This necessarily shortens the life of the heater section.
While the aforementioned U.S. Pat. No. 4,260,875 discloses the use of apertures in the mica boards in order to enhance air circulation within the dryer housing, this air circulation is helpful to more uniformly distribute temperature at the nozzle output, but nevertheless insufficient to efficiently distribute output temperature.
Consequently, it is an object of this invention to provide a heater secton capable of outputting an air flow having a more uniform temperature distribution. Also, it is another object to provide a heater section capable of generating sufficient amounts of heat at lower average operating currents and temperatures of resistance wire.